WT1 gene (Wilms' tumor 1 gene) is a gene which was identified as a gene responsible for Wilms tumor which is a renal cancer in children (Non-patent Documents 1 and 2). WT1 is a transcription factor having a zinc finger structure. Initially, WT1 gene was considered to be a tumor suppressor gene. However, subsequent studies (Non-patent Documents 3, 4, 5 and 6) showed that WT1 gene rather functions as an oncogene in hematopoietic tumors and solid cancers.
It was showed that peptide-specific cytotoxic T cells (CTLs) were induced by stimulating peripheral mononuclear cells in vitro using a WT1 peptide and that these CTLs damage tumor and cancer cells in hematopoietic tumors and solid cancers which express WT1 endogenously. Because CTL recognizes a WT1 peptide in a form of a complex in which the WT1 peptide is bound to a MHC class I molecule, such a WT1 peptide differs in accordance to MHC class I subtype (Patent Document 1, Non-Patent Document 7, Patent Documents 2, 3 and 4).
Existence of helper T cells specific to a cancer antigen is important for effective induction of CTL (Non-Patent Document 8). Helper T cells are induced and activated by recognizing a complex of a MHC class II molecule and an antigen peptide on antigen-presenting cells. Activated helper T cells produce cytokines such as IL-2, IL-4, IL-5, IL-6, or interferons, and help proliferation, differentiation and maturation of B cells. Activated helper T cells also have a function to promote proliferation, differentiation and maturation of other subset of T cells (such as Tc cells). Thus, because activated helper T cells have a function to activate immune system by promoting proliferation and activation of B cells and T cells, it is considered that enhancing the function of helper T cells via a MHC class II binding antigen peptide (helper peptide) to enhance the effect of a cancer vaccine is useful in cancer immunotherapy (Non-Patent Document 9).
Examples of helper peptides relating to WT1 which are presently recognized are a peptide binding to HLA-DRB1*04:01 molecule (Non-Patent Document 10), a peptide binding to HLA-DRB1*04:05 molecule, a peptide binding to HLA-DRB1*15:02 molecule (Patent Document 5), a peptide binding to HLA-DRB1*04:05 molecule, HLA-DRB1*15:02 molecule, HLA-DRB*15:01 molecule, HLA-DPB1*09:01 molecule and HLA-DPB1*05:01 molecule (Patent Document 6).
However, sequences of T cell receptor (TCR) genes of antigen-specific CD4+ helper T-cells which recognize a helper peptide have not been known at all.